Microlithographic projection exposure apparatus

ABSTRACT

The disclosure relates to a microlithographic projection exposure apparatus and a microlithographic projection exposure apparatus, as well as related components, methods and articles made by the methods. The microlithographic projection exposure apparatus includes an illumination system and a projection objective. The illumination system can illuminate a mask arranged in an object plane of the projection objective. The mask can have structures which are to be imaged. The method can include illuminating a pupil plane of the illumination system with light. The method can also include modifying, in a plane of the projection objective, the phase, amplitude and/or polarization of the light passing through that plane. The modification can be effected for at least two diffraction orders in mutually different ways. A mask-induced loss in image contrast obtained in the imaging of the structures can be reduced compared to a method without the modification.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e)(1) to U.S. Ser.No. 60/973,202, filed Sep. 18, 2007, and under 35 U.S.C. §119 to Germanpatent application 10 2007 044 678.2, filed Sep. 18, 2007. The entirecontents of these applications are incorporated herein by reference.

FIELD

The disclosure relates to a microlithographic projection exposureapparatus and a microlithographic projection exposure apparatus, as wellas related components, methods and articles made by the methods.

BACKGROUND

Microlithography is used for the production of microstructuredcomponents, such as, for example, integrated circuits or LCDs. Ingeneral, the microlithography process is carried out in what is referredto as a projection exposure apparatus having an illumination system anda projection objective. Generally, the mask (commonly referred to as areticle) is illuminated by the illumination system, and the image of themask is projected by the projection objective onto a substrate (forexample a silicon wafer). Typically, the substrate is coated with alight-sensitive layer (for example photoresist) which is arranged in theimage plane of the projection objective so that the mask structure istransferred onto the light-sensitive coating on the substrate, generallyreduced by a factor of 0.25.

SUMMARY

In some embodiments, the disclosure provides a microlithographicprojection exposure apparatus and a method of its operation that canprovide improved compensation of aberrations caused by mask structures.

In certain embodiments, the disclosure provides a method of operating amicrolithographic projection exposure apparatus. The apparatus has anillumination system and a projection objective. The illumination systemilluminates a mask arranged in an object plane of the projectionobjective. The mask has structures which that are to be imaged. Themethod includes illuminating a pupil plane of the illumination systemwith light. The method also includes modifying, in a plane of theprojection objective, the phase, amplitude and/or polarization of thelight passing through that plane. Modification is effected for at leasttwo diffraction orders in mutually different ways, whereby amask-induced loss in image contrast obtained in the imaging of thestructures is reduced compared to a method without the modification.

The method can involve separating from each other diffraction orderswhich are generated by points in mirror image symmetry relative to eachother in the pupil plane of the illumination system.

It is possible to set in the illumination system an illumination setting(a given intensity distribution in the pupil plane of the illuminationsystem) which is in point symmetry relationship with respect to thepupil center, but not in mirror image symmetry relationship with respectto a plane of symmetry of the structure which is to be imaged. Inaccordance with its definition, the edge of the pupil is defined by rayswhich are incident on the field plane (reticle plane) in the opticalsystem or the illumination system at the maximum aperture angle. Thatcan provide that different diffraction orders (in particular the zeroand the first diffraction orders) which are generated by the lightemanating from points which are in mirror image symmetrical relationshipwith each other in the pupil plane of the illumination system come tolie at different locations in a pupil plane of the projection objective.Consequently those diffraction orders can be modified separately orindependently of each other, by for example using an optical filterwhich, by way of its optically effective surface, has regions that canhave different influence on phase and/or amplitude for at least onepolarization direction.

In some embodiments, the modifying is carried out in such a way that fora first illumination direction a first interference image is obtainedand for a second illumination direction a second interference image isobtained, where a lateral offset between the first interference imageand the second interference images is reduced. In certain embodiments,the lateral offset is reduced to a value of not more than 5% (e.g., notmore than 2.5%) of a period of the first or second interference image.In some embodiments, the lateral offset is reduced at least by a factorof 2 (e.g., at least by a factor of 3, at least by a factor of 4).

The change or difference in the diffraction phase, if the half gratingperiod (or half pitch) is reduced down to approximately 100 nm, may, forexample, correspond to approximately 11% of the period of the structure.This is because the change or difference in the diffraction phasedirectly appears as lateral offset between the respective interferenceimages for two different illumination directions. In practice, suchlateral offsets in the range of approximately 10% can begin to havenegative effects on the result of the lithographic process or thetechnical application, respectively. In certain embodiments, thislateral offset is reduced to not more than 5% (e.g., not more than 2.5%)of the period of the structure.

In some embodiments, monopoles of the set illumination setting arearranged in mirror image symmetrical relationship with each other in thepupil plane of the illumination system and illuminate the mask atdifferent moments in time (e.g., only at different moments in time) witha time difference or a time interval ΔT therebetween. Then, in theexposure process, an altered phase, amplitude or polarizationmodification is produced after expiry of the time interval ΔT, in theprojection objective. That can be achieved via an optical filter byeither replacing the optical filter or by adjusting the optical filterwith respect to the arrangement of its region or regions which modifythe phase and/or amplitude.

The disclosure is not limited to replacing or adjusting an opticalfilter. For example, in some embodiments, the modification of phase,amplitude and/or phase shift, which is achieved after expiry of the timeinterval ΔT (or at the moment of illumination of the respective otherillumination pole of the set illumination setting) in the projectionobjective can also be implemented via a lens decentering procedure, alens displacement along the optical axis of the projection objective, alens tilting movement, a lens bending effect or by the manipulation of amirror surface in the projection objective. Local thermal changes inlenses due for example to IR radiation can also be used for amodification to the phase.

In some embodiments, an optical filter is used, which over its opticallyeffective surface has regions involving differing phase shift and/oramplitude influencing for at least one polarization direction. A changein polarization can be achieved, in the event of phase and/or amplitudebeing influenced in different ways, for various polarization directions.If the phase and/or amplitude for different polarization directions areinfluenced in the same manner in contrast that affords a purely scalarchange in transmission or change in phase without a change inpolarization.

In certain embodiments, the structures of the mask have at least onerepetition direction. In such embodiments, illuminating the pupil planeof the illumination system can be effected with an intensitydistribution which has two illumination poles.

In some embodiments, a connecting straight line between the centroids ofthe illumination poles are neither perpendicular nor parallel to therepetition direction.

In certain embodiments, an angle between the centroids of theillumination poles and the repetition direction is less than 45° (e.g.,less than 35°, less than 25°, less than 15°).

In some embodiments, in a pupil plane of the projection objective thefirst diffraction order of one illumination pole is located at least inclose neighborhood to the zero diffraction order of the otherillumination pole, and vice versa.

In certain embodiments, a characteristic width (which may in particularbe a half grating period also called half pitch, wherein pitch denotesthe period of the grid) of the structures on the mask to be imaged, isnot more than two times of the wavelength (e.g., not more than 1.4 timesof the wavelength, not more than 1.2 times of the wavelength, not morethan the wavelength) of the light used in the microlithography process.

In some embodiments, the characteristic width of the structures on themask to be imaged is not more than 300 nm (e.g., not more than 250 nm,not more than 200 nm). For a typical imaging scale of ¼, a half-pitchof, for example, 180 nm corresponds to a typical structure width of 45nm on the wafer. In such situations, the concept of the disclosure canbe particularly effective because the influence of aberrationsintroduced by the mask can become particularly noticeable withdecreasing grating period, such as when the structures on the mask to beimaged comes in the proximity of the wavelength of the light used in themicrolithography process.

In some embodiments, the disclosure provides a method of operating amicrolithographic projection exposure apparatus. The apparatus includesan illumination system and a projection objective. The illuminationsystem illuminates a mask arranged in an object plane of the projectionobjective. The mask has structures which are to be imaged. The methodincludes illuminating a pupil plane of the illumination system withlight. The method also includes modifying, in a plane of the projectionobjective, the polarization of the light passing through that plane. Themodification is effected for at least two diffraction orders in mutuallydifferent ways.

In certain embodiments, the disclosure provides an optical system of aprojection objective of a microlithographic projection exposureapparatus. The optical system includes an optical filter configured tomanipulate light passing through the optical filter. The positionaldependency of the manipulation caused by that optical filter can bedescribed by the equation:

M(x, y)=M(−x, −y)

where x and y denote positional co-ordinates in a plane of theprojection objective, and wherein M is a parameter characteristic of thelight passing through the optical filter. The parameter characteristicof the light passing through the optical filter can be the amplitude,phase or polarization of that light.

The disclosure relates to a microlithographic projection exposureapparatus, a process for the microlithographic production ofmicrostructured components, and a microstructured component.

Further configurations of the disclosure are set forth in thedescription, claims and figures. The disclosure is described in greaterdetail hereinafter by means of embodiments by way of example illustratedin the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIGS. 1 a-c show diagrammatic views to explain the effect of maskaberrations on the microlithography process,

FIGS. 2 a-b show diagrams by way of example illustrating calculateddependencies in respect of diffraction efficiency (FIG. 2 a) anddiffraction phase (FIG. 2 b) on half the grating period in the structureof a mask for different diffraction orders and different polarizationstates,

FIGS. 3 a-c show diagrammatic views to illustrate a method,

FIG. 4 shows a diagrammatic view of an optical filter,

FIG. 5 a-d show diagrammatic views to illustrate a method, and

FIG. 6 shows a diagrammatic view illustrating the structure in principleof a microlithographic projection exposure apparatus.

DETAILED DESCRIPTION

If the width of the structures on the mask is in the proximity of thewavelength of the light used in the microlithography process, the maskcan introduce aberrations because the diffraction orders can experiencea phase and amplitude change, the magnitude of which depends on theperiod of the mask structures.

FIG. 1 a illustrates a situation in which light is incident on a mask100 at two different directions of incidence identified by “A” and “B”respectively. Mask 100 has structures 102 (for example of chromium, Cr),arranged on a mask substrate 101 (for example of quartz glass, SiO₂).Diffraction orders occurring as a consequence of diffraction at thestructures 102 downstream of the mask 100 are denoted for the light fromthe direction of incidence A by A-0 (=zero diffraction order) and A-1(=first diffraction order), and for the light from the direction ofincidence B by B-0 (=zero diffraction order) and B-1 (=first diffractionorder). FIG. 1 b shows the intensity variation in dependence on thepositional coordinate x for the partial images respectively producedwith the light from the different directions of incidence A and B. FIG.1 c shows the intensity variation obtained by summing of those twopartial images. The total image afforded by addition of the two partialimages as shown in FIG. 1 c is of a contrast which is reduced incomparison with the individual partial images.

For a first different illumination direction A, an interference isobtained between the first diffraction order A-1 with the zerodiffraction order A-0, which produces a first interference image whichis labeled with “A” in FIG. 1 b. For a second illumination direction B,an interference is obtained between the first diffraction order B-1 withthe zero diffraction order B-0, which produces a second interferenceimage which is labeled with “B” in FIG. 1 b. The first and secondinterference images or partial images, respectively, are laterallydisplaced with respect to each other, i.e. have a lateral offset Δx,which can be seen in FIG. 1 b by comparison between the solid and dashedline. The lateral offset Δx corresponds to a fading or decreasedcontrast, as can be seen in FIG. 1 c, which can have negative effects.

FIG. 2 a and 2 b show, for the example of a binary chromium-quartz glassmask, the calculated dependency with respect to diffraction efficiency(in percent, FIG. 2 a) and diffraction phase (in degrees, FIG. 2 b) onhalf the grating period (in nm), in each case both for the zerodiffraction order and the first diffraction order as well as for twomutually orthogonal polarization states (TE and TM). The calculation wasimplemented by what is referred to as the RCWA theory. From theconfiguration of the respective curves in FIGS. 2 a and 2 b, it isapparent the effects of aberrations introduced by the mask become onlycomparatively slightly noticeable at a value of half the grating periodof about 500 nm (corresponding to a grating period of 1 μm) as thecurves represent approximately horizontal straight lines and also thedegree of deviation of the curves for respectively orthogonalpolarization states is slight. With a decreasing grating period therespective curves differ markedly from a straight-line configuration,while in addition there are marked differences for mutually orthogonalpolarization states.

Referring to FIG. 2 b, the change or difference in the diffractionphase, if the half grating period (or half pitch) is reduced down toapproximately 100 nm, has a value of roughly 40°. This value appears aslateral offset between the respective interference images for twodifferent illumination directions and corresponds to approximately 11%of the period. It can therefore be desirable to reduce this lateraloffset and the accompanying loss in image contrast.

FIGS. 3 a-c describe a method carried out in a microlithographicprojection exposure apparatus for which a structure by way of example isdescribed hereinafter with reference to FIG. 6.

FIG. 3 a diagrammatically shows an intensity distribution 310 which isset in a pupil plane of the illumination system (by using one or moresuitable pupil-forming elements, for example diffractive opticalelements). FIG. 3 b is a view in greatly simplified fashion of astructure 320 by way of example, as can be provided on a mask arrangedin the object plane of the projection objective. FIG. 3 c is also adiagrammatic view showing the arrangement of the zero and firstdiffraction orders obtained in a pupil plane of the projection objectiveby virtue of diffraction at the mask structure 320.

The intensity distribution in the pupil plane of the illuminationsystem, that is to say what is referred to as the illumination setting,includes as shown in FIG. 3 a precisely two illumination poles which aredenoted by “A” and “B” respectively and which in the pupil plane extendin point symmetrical relationship with a point on the optical axis ofthe illumination system, but which are not in mutually mirror imagesymmetrical relationship, with respect to an axis of symmetry of thestructure whose image is to be formed. In other words, a connecting linejoining the two illumination poles “A” and “B” does not extendperpendicularly to the structure direction (extending in the x-directionas shown in FIG. 3 b) of the mask structure 320.

As can be seen from FIG. 3 c the consequence of that choice of theillumination setting is that the different diffraction orders (inparticular the zero and first diffraction orders) which are produced asa consequence of diffraction of the light of the two illumination polesin the pupil plane of the projection objective come to lie at mutuallydifferent positions in the pupil plane of the projection objective. Theregion involving the zero diffraction order for the diffraction pole Ain FIG. 3 a is identified by “A-0”, the region of the first diffractionorder for the diffraction pole A is identified by “A-1”, the region ofthe zero diffraction order for the illumination pole B is denoted by“B-0” and the region of the first diffraction order for the illuminationpole B is denoted by “B-1”.

The regions “A-0”, “A-1”, “B-0” and “B-1” can be influenced in differentways from each other to at least partially compensate for maskaberrations. The influencing effect can be implemented with respect tothe phase and/or amplitude for at least one polarization direction.

FIG. 4 shows an example an optical filter 400 which is suitable for thatpurpose and which is made up of portions 410-440 which in the exampleare in the form of segments of a circle, in which case the portions 410and 420 have transmission and/or phase shift properties which aredifferent from the transmission and phase shift properties respectivelyof the regions 430 and 440. In filter 400 the phase shift properties ofthe regions 410 and 420 (and the regions 430 and 440 respectively) arerespectively mutually coincident.

FIG. 5 a and FIG. 5 c show illumination poles 511 and 521 which areproduced in a pupil plane of the illumination system in such a way thatthey are arranged both in point symmetrical relationship with a point onthe optical axis of the illumination system and also in mutually mirrorimage symmetrical relationship with respect to a plane intersecting thatoptical axis or with respect to an axis of symmetry of the structure,the image of which is to be produced.

Illumination of illumination poles 511 and 521 occurs not at the sametime but at different moments in time or at different field points inthe scanning operation. At the different moments in time, the phase,amplitude and/or polarization are manipulated differently in theprojection objective. As an example, an optical filter can be used inthe projection objective for this purpose. In such embodiments, in thetime interval between the two moments in time, the optical filter caneither be replaced or can be adjusted with respect to the arrangement ofits regions that manipulate amplitude, phase or polarization. FIG. 5 bshows an example in which an optical filter 530 is used in theprojection objective during exposure with the illumination setting ofFIG. 5 a. FIG. 5 d shows an example where an optical filter 540 is usedduring exposure with the illumination setting of FIG. 5 c. Opticalfilters 530 and 540 differ from each other with respect to thetransmission and/or phase shift they produce.

In some embodiments, time-displaced exposure with different illuminationsettings can be implemented as follows. The wafer is exposed using afirst illumination setting. There is then a change in the illuminationsetting and an optical filter, and the wafer is exposed using a secondillumination setting. Typical change rates can be in the seconds range.If a through-put rate of, for example, 120 wafers per hour with singleexposure is assumed to apply, a change in the optical filter can takeplace in terms of order of magnitude, for example, every 30 seconds.

WO 2006/097135 A1 discloses arrangements for and methods of rapidlychanging illumination settings. Similar methods can be used for a rapidchange of an optical filter, for example in a pupil plane of theprojection objective. US No 2007/0153247 A1 or US No 2005/0213070 A1disclose systems in which the scanner slot can be divided into tworegions so as to make different pupil regions or planes manipulatableseparately. Such systems can be implemented in the system describedherein.

FIG. 6 is a purely diagrammatic view showing a structure in principleand by way of example of a microlithographic projection exposureapparatus. The microlithographic projection exposure apparatus has anillumination system 601 and a projection objective 602. The illuminationsystem 601 serves for illuminating a structure-bearing mask (reticle)603 with light from a light source unit 604 which for example includesan ArF laser for a working wavelength of 193 nm as well as a beamshaping optical mechanism for producing a parallel light beam. Theparallel light beam of the light source unit 604 is firstly incident ona diffractive optical element 605 which, by way of an angle radiationcharacteristic defined by the respective diffractive surface structure,produces in a pupil plane P1 a desired intensity distribution (forexample dipole or quadrupole distribution). Disposed downstream of thediffractive optical element 605 in the light propagation direction is anoptical unit 606 including a zoom objective for producing a parallellight beam of variable diameter, and an axicon lens. Differentillumination configurations are produced by the zoom objective inconjunction with the upstream-disposed diffractive optical element 605in the pupil plane P1 depending on the respective zoom position and theposition of the axicon elements. In the illustrated embodiment theoptical unit 606 further includes a deflection mirror 607. Disposeddownstream of the pupil plane P1 in the light propagation direction inthe beam path is a light mixing device 608 which for example in per seknown manner can have an arrangement of microoptical elements that issuitable for achieving a light mixing effect. The light mixing device608 is followed in the light propagation direction by a lens group 609,downstream of which is disposed a field plane F1 with a reticle maskingsystem (REMA) which is projected by an REMA objective 610 following inthe light propagation direction onto the structure-bearing mask(reticle) 603 arranged in the field plane F2 and thereby limits theilluminated region on the reticle. The image of the structure-bearingmask 603 is formed with the projection objective 602 which in theillustrated embodiment has two pupil planes PP1 and PP2, on a substrate611 or a wafer provided with a light-sensitive layer.

While certain embodiments have been described, it will be appreciated byone skilled in the art that variations and alternatives are possible.

1. A method, comprising: providing a microlithographic projectionexposure apparatus having an illumination system and a projectionobjective; illuminating a pupil plane of the illumination system withlight; and modifying, in a plane of the projection objective, at leastone parameter of the light passing through the plane of the projectionobjective, wherein: the at least one parameter is selected from thegroup consisting of a phase of the light, an amplitude of the light anda polarization of the light; and at least two diffraction orders of thelight are modified in mutually different ways so that a mask-inducedloss in image contrast obtained in the imaging of the structures isreduced compared to performing the method without modifying the at leastone parameter.
 2. The method as set forth in claim 1, wherein a lateraloffset between a first interference image and a second interferenceimage is reduced compared to performing the method without modifying theat least one parameter, the first interference image being obtained in afirst illumination direction, and the second interference image beingobtained in a second illumination direction.
 3. A method as set forth inclaim 2, wherein the lateral offset is not more than 5% of a period ofthe first interference image or second interference image.
 4. A methodas set forth in claim 2, wherein the lateral offset is reduced at leastby a factor of 2 compared to performing the method without modifying theat least one parameter.
 5. A method as set forth in claim 1, wherein themask has structures, and the pupil plane of the illumination system isilluminated with an intensity distribution that is not in mirror imagesymmetrical relationship with respect to a plane of symmetry of thestructures.
 6. A method as set forth in claim 1, wherein the pupil planeof the illumination system is illuminated with an intensity distributionwhich is in point symmetrical relationship with respect to a center ofthe pupil plane.
 7. A method as set forth in claim 1, wherein an opticalfilter with an optically effective surface is used to modify the atleast one parameter, and the optically effective surface of the opticalfilter has regions capable of having different influence on a phaseshift and/or an amplitude for at least one polarization direction.
 8. Amethod as set forth in claim 1, wherein the mask has structures with arepetition direction, and the pupil plane of the illumination system isilluminated with an intensity distribution which has two illuminationpoles.
 9. A method as set forth in claim 8, wherein a connectingstraight line between centroids of the illumination poles is neitherperpendicular nor parallel to the repetition direction.
 10. A method asset forth in claim 8, wherein an angle between the centroids of theillumination poles and the repetition direction is less than 45°.
 11. Amethod as set forth in claim 8, wherein, in a pupil plane of theprojection objective, a first diffraction order of one illumination poleis located at least in close neighborhood to a zero diffraction order ofthe other illumination pole, and vice versa.
 12. A method as set forthin claim 1, wherein the pupil plane of the illumination system isilluminated so that at least two regions arranged in mirror imagesymmetrical relationship with each other in the pupil plane of theillumination system are illuminated at different moments in time.
 13. Amethod as set forth in claim 12, wherein the phase and/or the amplitudeis modified for at least one polarization direction at the differentmoments in time in mutually different ways.
 14. A method as set forth inclaim 12, wherein, at the different moments in time, an optical filteris replaced or adjusted to modify the phase and/or the amplitude.
 15. Amethod as set forth in claim 1, wherein the at least one parameter ismodified in a pupil plane of the projection objective.
 16. A method asset forth in claim 1, wherein the at least one parameter is modifiedusing an optical filter.
 17. A method as set forth in claim 16, whereinthe optical filter has a transmission T with a positional dependencydescribed by the equation:T(x, y)=T(−x, −y) where x and y denote positional co-ordinates in theplane of the projection objective.
 18. A method as set forth in claim16, wherein the optical filter has a phase shift (p with a positionaldependency described by the equation:φ(x, y)=φ(−x, −y) where x and y denote positional co-ordinates in theplane of the projection objective.
 19. A method as set forth in claim 1,wherein the at least two different diffraction orders are the zerodiffraction order and the first diffraction order.
 20. A method as setforth in claim 1, wherein modifying the at least one parameter includesat least one of the following: decentering at least one optical elementin the projection objective; displacing at least one optical elementalong an optical axis of the projection objective; tilting at least oneoptical element in relation to an optical axis of the projectionobjective; manipulating at least one mirror surface in the projectionobjective; deforming at least one optical element in the projectionobjective; and locally heating of at least one optical element in theprojection objective.
 21. A method as set forth in claim 1, wherein acharacteristic width of structures on the mask is not more than twotimes a wavelength of the light.
 22. A method as set forth in claim 1,wherein a characteristic width of structures on the mask is not morethan 300 nm.
 23. A method as set forth in claim 21, wherein thecharacteristic width is a half grating period of the structures on themask.
 24. A method, comprising: providing a microlithographic projectionexposure apparatus having an illumination system and a projectionobjective; illuminating a pupil plane of the illumination system withlight; and modifying, in a plane of the projection objective, apolarization of the light passing through the plane of the projectionobjective, wherein at least two diffraction orders of the light aremodified in mutually different ways.
 25. A method as set forth in claim24, wherein a mask-induced loss in image contrast obtained in themicrolithographic operation is reduced compared to performing the methodwithout modifying the polarization of the light passing through theplane of the projection objective.
 26. An optical system, comprising: anoptical filter configured to be used in a projection objective of amicrolithographic projection exposure apparatus, the optical filter tomanipulate light passing therethrough, wherein a positional dependencyof the manipulation of the light caused by the optical filter isdescribed by the equation:M(x, y)=M(−x, −y) where x and y denote positional co-ordinates in aplane of the projection objective and wherein M is a parametercharacteristic of the light passing through the optical filter.
 27. Anoptical system as set forth in claim 26, wherein the parameter isselected from the group consisting of an amplitude of the light, a phaseof the light and a polarization of the light.
 28. An optical system asset forth in claim 26, wherein the optical filter has a transmission Twith a positional dependency described by the equation:T(x, y)=T(−x, −y) where x and y denote positional co-ordinates in theplane of the projection objective.
 29. An optical system as set forth inclaim 26, wherein the optical filter has a phase shift φ with apositional dependency described by the equation:φ(x, y)=φ(−x, −y) where x and y denote positional co-ordinates in aplane of the projection objective.
 30. An apparatus, comprising: anoptical filter configured to manipulate light passing therethrough, apositional dependency of the manipulation of the light caused by theoptical filter is described by the equation:M(x, y)=M(−x, −y) where x and y denote positional co-ordinates in aplane of the projection objective and wherein M is a parametercharacteristic of the light passing through the optical filter, whereinthe apparatus is a microlithographic projection exposure apparatus. 31.A process, comprising: using the apparatus of claim 30 to producemicrostructured components.